The present invention relates to a jacquard type loom.
FIG. 1 is a diagram of a jacquard type loom 10 used for making fiber structures or fabric obtained by multilayer weaving between a plurality of layers of warp yarns 30 and a plurality of layers of weft yarns 31.
In known manner, the loom 10 is fitted with a jacquard mechanism 11 supported by a superstructure that is not shown in FIG. 1. The loom 10 also has a harness 20 constituted by a comber board 21 and control cords or heddles 22, each heddle 22 being connected at one end to a control hook 12 of the jacquard mechanism 11 and at the other end to one of the return springs 13 fastened to the base 14 of the loom 10.
Each heddle 22 includes a heddle eye 23 having a warp yarn 30 passing therethrough. The heddles 22 and their associated heddle eyes 23 are driven in substantially vertical reciprocating motion represented by double-headed arrow F under traction forces exerted respectively by the control hooks 12 and by the return springs 13. The heddles 22 serve to lift certain warp yarns 30, thereby creating a shed 15 enabling weft yarns 31 to be inserted.
The heddles 22 are distributed in space as a function of the positions of the holes 210 of the comber board 21, i.e. in a plurality of columns 211 and rows 212.
The density of the holes 210 in the comber board corresponds to the density in the fabric to be made, i.e. the spacing between each of the columns of holes in the comber board is equivalent to the spacing that is presented between each of the warp columns in the fabric that is to be made.
Certain fiber structures, e.g. such as those for constituting the reinforcement of aeroengine blades made of composite material, require weaving that is very dense, with a thread count, and in particular a warp thread count, that is relatively tight in order to confer good mechanical strength to the part. The warp thread count corresponds to the number of warp yarns per unit length. Consequently, when it is desired to weave with a tighter thread count, it is necessary to reduce the spacing between the columns of holes in the comber board, thereby causing the heddles of a column, e.g. the heddles 22 of the column l1 to be closer to the heddles of the adjacent column(s), e.g. here the column l2. Nevertheless, when the heddles of two adjacent columns are too close together, then the movements of the heddles, and more particularly of their associated heddle eyes, are impeded by the proximity of the heddles and of the warp yarns present in the adjacent column.
In order to avoid any risk of catching between heddles belonging to adjacent columns, it is necessary to ensure some minimum amount of spacing between the heddle columns. There is thus a limit on the extent to which the density of the thread count of a fabric can be increased with existing looms.